Udo D. Schwarz

We identify the local structural defects that control the nonaffine displacement fields in jammed disk packings subjected to athermal, quasistatic simple shear. While complex nonaffine displacement fields typically occur during simple shear, isolated effective quadrupoles are also observed and their probability increases with increasing pressure. We show that the emergence of an isolated effective quadrupole requires the breaking of an interparticle contact that is aligned with low-frequency, spatially extended vibrational modes. Since the Eshelby inhomogeneity problem gives rise to quadrupolar displacement fields in continuum materials, we reformulate and implement Eshelby's equivalent inclusion method (EIM) for jammed disk packings. Using EIM, we show that we can reconstruct the nonaffine displacement fields for jammed disk packings in response to applied shear as a sum of discrete Eshelby-like defects that are caused by mismatches in the local stiffnesses of triangles formed from Delaunay triangulation of the disk centers.

Plastic deformation of Mg x Li1Zn0.5Ca ( x = 0, 4, 8, 11) alloys after thermomechanical treatment were explored in this investigation. Nanomechanical testing and microstructural characterization were conducted on as-cast alloys as well as those rolled at room temperature and 200 °C. The grain size of the 0 wt% Li alloy decreased after cold and hot rolling, whereas that for alloys with 11 wt% Li content decreased after rolling at 200 °C. Additionally, reorientation of crystallographic planes occurred as evidenced by changes in peak intensity of prismatic, basal and pyramidal planes of x-ray diffractograms. The hardness and yield strength of both as-cast and rolled alloys increased after rolling, especially for alloys containing the α-Mg phase. Furthermore, the single β-phase had a strain rate sensitivity of 0.06 and an activation volume greater than 10 7 nm 3 . These results suggest that the dominant deformation mechanisms include basal slipping, twinning and cross slipping. The combined studies of deformation mechanism and thermomechanical processing offered a robust method to understand the Mg alloys' plastic behavior.

Antibacterial Coatings In article 2400895, Amin Bahrami and co-workers, demonstrate that a 3D-printed FeMnC biodegradable alloy can be effectively coated with antibacterial ALD-ZnO. The ALD-ZnO coating exhibited superior antibacterial performance against Gram-positive Staphylococcus aureus compared to both the uncoated Fe69Mn30C1 alloy and clinically used 316L stainless steel. Art by the team of INMYWORK Studio.

Supported cobalt phthalocyanines (CoPc) are promising catalysts for CO 2 reduction, a critical process for mitigating greenhouse gas emissions. Enhancing the catalytic performance of CoPc involves modifying the interaction between the cobalt center and intermediate species. This study focuses on the effects of tert -butyl substitution on CoPc using ( tert -butyl) 4 CoPc, where the substitution can both directly alter the molecule’s intramolecular electronic structure and indirectly alter it by the bulky group weakening the interaction with the support. Toward this end, we investigated the structural and chemical properties of ( tert -butyl) 4 CoPc on a Ag(111) surface at the single-molecule level using three-dimensional atomic force microscopy (AFM) with a CO-terminated tip and discussed them in comparison with data for unmodified CoPc and amino-substituted CoPc. Notably, distance-dependent force measurements revealed anomalies in the tert -butyl groups’ force curves, attributed to their rotational flexibility. The tert -butyl ( t -butyl) groups were also observed to increase the attraction of the central Co atom to CO, but this effect was attributed largely to enhanced interactions of the back of the tip with the peripheral t -butyl groups. While this longer-range interaction would not be expected to impact the interaction of small molecules with the catalytic center, the results reveal the ability of AFM to characterize longer range environmental interactions that can enhance adsorption and subsequent reactions of larger molecules, as well as the role side chains that offer configurational adaptability may play in these interactions.

Although the enhanced structural relaxation is usually believed to be an important contributor to work hardening of metallic glasses subjected to triaxial stress state, an direct observation of relaxation process in response to work hardening has not been achieved in metallic glasses. Here we show that by nanoscratching on an atomically flat bulk metallic glass surface, the small atomic force microscopy tip with a radius of ≈ 10 nm brings about a large hydrostatic stress within stressed volume, which enables a densifying plastic flow via enhanced structural relaxation and leads to the work hardening behavior, as evidenced by an obvious decrease in friction force signals within scratched regions. Further examination on the atomic structure beneath the scratched surface using high resolution transmission electron microscopy reveals a relaxed structural configuration, which is indicated by disperse clusters of medium-range order scale in the case of line scratching and nucleated nanocrystals in the case of cyclic scratching. This study provides a compelling evidence for stress-driven structural relaxation, greatly deepening the understanding of work hardening mechanism in metallic glasses.

Abstract As implant‐related infections increase with a simultaneously increasing demand for implants, new material design concepts are needed to prevent such occasions from leading to failure or mortality. One approach is the antibacterial coating of implant materials with ZnO. This study applies ZnO by atomic layer deposition (ALD) on the novel class of temporary metallic implant materials. The biodegradable alloy Fe69Mn30C1 is applied as substrate. Three different coating thicknesses (33, 45, and 60 nm) deposited at the very low temperature of 100 °C are investigated regarding their mechanical behavior, roughness, wettability and in vitro degradation. With increasing thickness of the ALD coating, the roughness and corresponding contact angle slightly increased, although the surface remained hydrophilic. Initial corrosion products are analyzed by X‐ray photoelectron spectroscopy, where Zn with Phosphorous‐Oxygen compounds are identified. Furthermore, the antibacterial effect of a ZnO coating is tested against Gram‐positive Staphylococcus aureus compared to uncoated Fe69Mn30C1 and clinically applied 316L stainless steel. The ZnO coating clearly enhanced the antibacterial effect in direct material contact with S. aureus , inhibitory rate of up to 99.2% compared to uncoated 316L. As an outlook for further studies, it is demonstrated that an additively manufactured generic 3D structure can be coated using ALD.

Abstract In alignment with the Materials Genome Initiative and as the product of a workshop sponsored by the US National Science Foundation, we define a vision for materials laboratories of the future in alloys, amorphous materials, and composite materials; chart a roadmap for realizing this vision; identify technical bottlenecks and barriers to access; and propose pathways to equitable and democratic access to integrated toolsets in a manner that addresses urgent societal needs, accelerates technological innovation, and enhances manufacturing competitiveness. Spanning three important materials classes, this article summarizes the areas of alignment and unifying themes, distinctive needs of different materials research communities, key science drivers that cannot be accomplished within the capabilities of current materials laboratories, and open questions that need further community input. Here, we provide a broader context for the workshop, synopsize the salient findings, outline a shared vision for democratizing access and accelerating materials discovery, highlight some case studies across the three different materials classes, and identify significant issues that need further discussion. Graphical abstract

Tissue mechanical properties are determined mainly by the extracellular matrix (ECM) and actively maintained by resident cells. Despite its broad importance to biology and medicine, tissue mechanical homeostasis remains poorly understood. To explore cell-mediated control of tissue stiffness, we developed mutations in the mechanosensitive protein talin 1 to alter cellular sensing of ECM. Mutation of a mechanosensitive site between talin 1 rod-domain helix bundles R1 and R2 increased cell spreading and tension exertion on compliant substrates. These mutations promote binding of the ARP2/3 complex subunit ARPC5L, which mediates the change in substrate stiffness sensing. Ascending aortas from mice bearing these mutations showed less fibrillar collagen, reduced axial stiffness, and lower rupture pressure. Together, these results demonstrate that cellular stiffness sensing contributes to ECM mechanics, directly supporting the mechanical homeostasis hypothesis and identifying a mechanosensitive interaction within talin that contributes to this mechanism.

This study provides a comprehensive analysis of a Ti-42Nb alloy produced via laser powder bed fusion (LPBF) with varying post-heat treatment durations within the α + β phase range at 723 K. Synchrotron XRD analysis revealed the formation of the metastable orthorhombic αiso′′ phase during heat treatment, acting as an intermediate to the stable α phase. With prolonged heat treatment, the αiso′′ phase fraction increased, reaching approximately 25 % after 108.0 ks. SEM analysis identified β grain boundaries as primary sites for early αiso′′ precipitation, while intragranular αiso′′ precipitation was delayed. Up to 28.8 ks, volume fraction and size of intragranular precipitates exhibited notable variations due to minor Nb content fluctuations from LPBF processing, resulting in an increased spread of hardness and Young's modulus on the micro scale. Tensile tests revealed significant strength enhancement through post-heat treatment for 108 ks, achieving a yield strength of around 1060 MPa (50 % increase) and ultimate tensile strength of 1125 MPa (55 % increase) compared to the as-built state. Extended growth of the αiso′′ phase led to an increased Young's modulus, reaching 87 GPa after 108.0 ks. These findings provide valuable insights for developing post-heat treatment strategies for LPBF-produced Ti-42Nb implants, including both bulk materials and lattice structures.

Recent advances in scanning probe microscopy methodology have enabled the measurement of tip–sample interactions with picometer accuracy in all three spatial dimensions, thereby providing a detailed site-specific and distance-dependent picture of the related properties. This paper explores the degree of detail and accuracy that can be achieved in locally quantifying probe–molecule interaction forces and energies for adsorbed molecules. Toward this end, cobalt phthalocyanine (CoPc), a promising CO 2 reduction catalyst, was studied on Ag(111) as a model system using low-temperature, ultrahigh vacuum noncontact atomic force microscopy. Data were recorded as a function of distance from the surface, from which detailed three-dimensional maps of the molecule’s interaction with the tip for normal and lateral forces as well as the tip–molecule interaction potential were constructed. The data were collected with a CO molecule at the tip apex, which enabled a detailed visualization of the atomic structure. Determination of the tip–substrate interaction as a function of distance allowed isolation of the molecule–tip interactions; when analyzing these in terms of a Lennard–Jones-type potential, the atomically resolved equilibrium interaction energies between the CO tethered to the tip and the CoPc molecule could be recovered. Interaction energies peaked at less than 160 meV, indicating a physisorption interaction. As expected, the interaction was weakest at the aromatic hydrogens around the periphery of the molecule and strongest surrounding the metal center. The interaction, however, did not peak directly above the Co atom but rather in pockets surrounding it.

Experimental data on compressive strength ${\ensuremath{\sigma}}_{\mathrm{max}}$ versus strain rate ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\ensuremath{\varepsilon}}}_{\mathrm{eng}}$ for metallic glasses undergoing uniaxial compression show varying strain rate sensitivity. For some metallic glasses, ${\ensuremath{\sigma}}_{\mathrm{max}}$ decreases with increasing ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\ensuremath{\varepsilon}}}_{\mathrm{eng}}$, while for others, ${\ensuremath{\sigma}}_{\mathrm{max}}$ increases with increasing ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\ensuremath{\varepsilon}}}_{\mathrm{eng}}$, and for certain alloys ${\ensuremath{\sigma}}_{\mathrm{max}}$ versus ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\ensuremath{\varepsilon}}}_{\mathrm{eng}}$ is nonmonotonic. To understand their strain rate sensitivity, we conduct molecular dynamics simulations of metallic glasses undergoing uniaxial compression at finite strain rates and coupled to heat baths with a range of temperatures ${T}_{0}$ and damping parameters $b$. In the ${T}_{0}\ensuremath{\rightarrow}0$ and $b\ensuremath{\rightarrow}0$ limits, we find that the compressive strength ${\ensuremath{\sigma}}_{\mathrm{max}}$ versus temperature $T$ obeys a ``chevron-shaped'' scaling relation. In the low-strain-rate regime, ${\ensuremath{\sigma}}_{\mathrm{max}}$ decreases linearly with increasing $T$, whereas ${\ensuremath{\sigma}}_{\mathrm{max}}$ grows as a power law with decreasing $T$ in the high-strain-rate regime. For ${T}_{0}>0, {\ensuremath{\sigma}}_{\mathrm{max}}(T)$ deviates from the scaling curve at low strain rates, but ${\ensuremath{\sigma}}_{\mathrm{max}}(T)$ rejoins the scaling curve as the strain rate increases. Enhanced dissipation reduces compression-induced heating, which causes ${\ensuremath{\sigma}}_{\mathrm{max}}(T)$ to deviate from the $b\ensuremath{\rightarrow}0$ scaling behavior for intermediate strain rates, but ${\ensuremath{\sigma}}_{\mathrm{max}}(T)$ converges to the high-strain-rate power-law scaling behavior at sufficiently high strain rates. Determining ${\ensuremath{\sigma}}_{\mathrm{max}}(T)$ as a function of $b$ and ${T}_{0}$ provides a general framework for explaining the strain rate sensitivity of metallic glasses under compression.

It is widely believed that tissue mechanical properties, determined mainly by the extracellular matrix (ECM), are actively maintained. However, despite its broad importance to biology and medicine, tissue mechanical homeostasis is poorly understood. To explore this hypothesis, we developed mutations in the mechanosensitive protein talin1 that alter cellular sensing of ECM stiffness. Mutation of a novel mechanosensitive site between talin1 rod domain helix bundles 1 and 2 (R1 and R2) shifted cellular stiffness sensing curves, enabling cells to spread and exert tension on compliant substrates. Opening of the R1-R2 interface promotes binding of the ARP2/3 complex subunit ARPC5L, which mediates the altered stiffness sensing. Ascending aortas from mice bearing these mutations show increased compliance, less fibrillar collagen, and rupture at lower pressure. Together, these results demonstrate that cellular stiffness sensing regulates ECM mechanical properties. These data thus directly support the mechanical homeostasis hypothesis and identify a novel mechanosensitive interaction within talin that contributes to this mechanism.

Techniques for operating an atomic force microscope, the atomic force microscope comprising a cantilever and configured to image a surface of a sample using a probe tip coupled to the cantilever, the techniques comprising using a controller to perform: obtaining, based on at least one intrinsic parameter of the cantilever, a first quality factor and a first free oscillation amplitude, wherein the cantilever exhibits only one stable oscillation state when oscillating at the first free oscillation amplitude and operating at the first quality factor; and controlling the cantilever to exhibit the only one stable oscillation state by controlling the cantilever to oscillate at a fixed frequency at or near a resonance frequency of the cantilever, oscillate at the first free oscillation amplitude, and operate at the first quality factor.